A Chemically Doped Phenylene Vinylene Polymer with High Electron Conductivity

High-performing organic materials are required for efficient opto-, bioelectronic and thermoelectric applications. Among these materials, (semi-)conducting polymers are particularly appealing for these technologies, as they benefit from unique optoelectronic properties, low-cost production and their solution processability make them fully compatible with large-scale deposition methods. The most common way to reach high electrical conductivities with this class of materials is to dope the polymers through the addition of a heterogeneous doping entities to the system.<br/>With the goal to produce highly-performing materials, huge efforts have been provided by the scientific community, notably through molecular design adjustments of these active materials. A current strategy towards this end is the planification and the rigidification of the polymer backbone, leading to a higher degree of order through a favorable molecular packing while decreasing the energetic disorder. This is the case, for example, for poly(p-phenylene vinylene) derivatives that benefit from both carbon-carbon double bonds between polymer units and intramolecular hydrogen bonds.<br/>Another way of enhancing the performances of (semi)conducting polymers is to increase the microscopic order and then the crystallinity of the polymeric assembly by adjusting the processing of deposition. One way to do so is to use Langmuir-Schaefer (LS) technique that relies on the assembly of the polymer chains at the air/water interface when compressed between two moving barriers. The assembled film composed by a monolayer of polymers with a low degree of defect is then transferred onto a substrate integrating electrodes to make a fully functional device.<br/>Here we report on LS films that are highly ordered and oriented at the monolayer limit. This describes a microscopic structure that is optimized for the transport of charges with strong anisotropic properties of electron conduction. Through a systematic analysis including scanning probe microscopy, optical spectroscopy, GIWAXS, and electrical measurements, we characterized the system in terms of structure, packing, energetics, and thermoelectric properties. We further optimized the electrical performances of the film when doping it with different molecular entities through secondary doping mechanisms, reaching n-type conductivities up to 4 S cm^-1, and a power factor of 1.5 µW m^-1 K^-2. Finally, we integrated this system as active material in organic electrochemical transistors (OECT) to study the penetration of ions within this structured thin-film to optimize the transconductance of these devices.